The present invention relates generally to sensors, and more particularly to sensors for detecting and measuring a medium.
Grinder pumps are often used in low pressure sewage systems for pumping sewage. The grinder pumps include a grinder mechanism for cutting or grinding solids or semisolid matter in the sewage being pumped. Grinding solids and/or semisolid matter in the sewage allows the resulting particulate effluent to be transferred using a pump through small diameter pipes without clogging.
Grinder pump systems are typically equipped with level sensors and an alarm. When the sewage reaches a certain level in the tank, the pump automatically switches on and when the sewage in the tank falls below a certain level, the pump automatically turns off. If the level rises too high, typically another sensor activates an alarm.
Conventional level sensors include, for example, mechanical float switches, sensing tubes connected to a pressure transducer, ultrasonic transducers, and capacitive level sensors.
One type of capacitive level sensor detects capacitance changes by means of vertical electrodes, one of which may be a continuous probe, and the other, a separate grounded probe or the grounded conductive wall of the tank containing the medium. With this type of capacitive level sensor, the absolute capacitance of the sensor is measured. The capacitance of the sensor is approximately proportional to the level of the medium in the tank. A drawback with this type of sensor is that the sensor is dependent upon the type of medium being measured. This is a problem when measuring the level of mediums having different dielectric constants and/or when the medium""s dielectric constant varies over time.
Another capacitive level sensor includes a plurality of conductive plates, along with a separate grounded probe or the grounded conductive wall of the tank containing the medium. Each of the conductive plates allows generating a voltage corresponding to the capacitance of the conductive plates and the medium disposed therebetween. A problem with capacitive level sensors is that a buildup of material on the sensor can affect the accuracy of the sensor in measuring the level of the medium.
There is a need for further capacitive sensors for detecting a medium, measuring a level of a medium, and measuring a level of the medium where there is a buildup on the sensor.
The present invention provides, in a first aspect, a sensor for use in determining a level of a medium. The sensor includes a first plurality of spaced-apart electrically conductive members disposed on a nonconductive support. Means are provided for selectively generating a first plurality of signals each having a frequency based on a capacitive value due to a respective conductive member of the first plurality of conductive members, an at least one ground member, and at least one of an absence of the medium and a presence of the medium. Means are also provided for enabling determination of the level of the medium based on frequencies of the first plurality of signals.
The present invention provides, in a second aspect, a sensor for use in determining a level of a medium. The sensor includes a first plurality of spaced-apart electrically conductive members disposed on a nonconductive support. Means are provided for enabling determination of the level of the medium based on capacitive values due to respective conductive members of the first plurality of conductive members, an at least one ground member, and at least one of an absence of the medium and a presence of the medium. The means for enabling determination of the level of the medium also includes means for compensating for buildup of a material on the sensor.
The present invention provides, in a third aspect, a sensor for use in determining a level of a medium. The sensor includes a first plurality of spaced-apart electrically conductive members disposed on a nonconductive support. The first plurality of conductive members are spaced-apart a first distance therebetween. A second plurality of conductive members is disposed on the nonconductive support, and the second plurality of conductive members is spaced from the first plurality of conductive members a second distance which is different from the first distance. First means is provided for enabling determination of the level of the medium based on capacitive values due to respective conductive members of the first plurality of conductive members, an at least one ground member, and at least one of an absence of the medium and a presence of the medium. In addition, second means enable determination of at least one of the presence of the medium and the level of the medium based on capacitive values due to respective conductive members of the second plurality of conductive members, the at least one ground, and at least one of an absence of the medium and a presence of the medium. Means for generating an alarm signal is provided based on the second means for enabling determination of the at least one of the presence of the medium and the level of the medium.
The present invention provides, in a fourth aspect, a sensor for use in detecting an object. The sensor includes a first plurality of spaced-apart electrically conductive members disposed on a nonconductive support. First means are provided for generating a first plurality of signals each having a frequency based on a capacitive value due to a respective conductive member of the first plurality of conductive members, an at least one ground member, and at least one of an absence of the object and a presence of the object. First means are also provided for enabling detection of the object based on frequencies of the first plurality of signals.
Methods for measuring a level of a medium and detecting an object are also disclosed.